The present invention relates to thermoformable acoustical mat compositions. More specifically the present invention relates to thermoformable mat compositions which have high filler concentrations and contain asphalt and a low content of both EVA and rubber elastomers thereby reducing the cost of the composition.
Sound deadening compositions have been used in vehicles such as passenger cars and trucks, commercial trucks and the like for many years. Types of compositions used in sound insulation vary from standard insulation types such as fiberglass mattings to coating type sound deadeners which may be sprayed or brushed onto various areas of a vehicle to provide sound deadening characteristics.
In certain applications a thicker more dense composition may be required than that which may be acquired using either normal insulation or coating type compositions. These compositions are sometimes referred to as acoustical mats. Acoustical mats are sheets of sound deadener material placed advantageously in the vehicle or automobile for protection of the interior from undesirable sound.
Acoustical mat compositions which are presently used in automotive or other vehicle applications are generally one of two types. In one type of acoustical mat it is desired to have direct contact and bonding between the mat and a body panel such that the mat attenuates panel resonance type sounds due to road vibrations and the like. Generally compositions which are useful in such a mat are heat bondable compositions which provide controlled wilting and bonding to the body panel, when the body panel with the composition attached thereto is heated during a paint cycle or the like. A second type of acoustical mat composition is a thermoformable acoustical mat. These compositions are designed such that they may be adhered to a backing substrate such as a foam, shoddy or mat material after they are thermoformed into a contoured shape or in situ during the thermoforming process. These compositions act to attenuate sound noises such as road noises, engine noises and the like.
The heat bondable mat compositions require controlled flow characteristics in a given temperature range such that they may conform to the shapes which they are designed to bond to during the heating process. Heat bondable mat compositions also require the capability for heat bonding to the body panel material when in position and at the time of heating. A third characteristic of these heat bondable materials is sound attenuation capability which of course must be up to specification as with any sound attenuator. Physical characteristics such as the low temperature stress characteristics and the second order temperature of the asphalt are also important characteristics in the heat bondable materials.
Thermoformable acoustical mat compositions, on the other hand, require much more stringent physical properties than the heat bondable mat compositions. Thus, good properties of tensile strength, elongation, modulus, controlled stiffness, controlled specific gravity, resistance to shrinking, low temperature flexibility, low flammability and the low staining properties are all important in a thermoformable composition. The necessity of these increased physical properties is because these materials must be thermoformed into and retain their contoured shapes with minimal shrinkage. These materials also require good adhesive capability for attachment of substrate insulating materials such as shoddy materials, resinous mat materials, and urethane foam substrates which are used between this material and the underlying sheet metal surface. Thus, the thermoformable acoustical mat materials must act as a relatively rigid skeleton member in order to retain the shape and give structural firmness to the backing material.
Because of the lower physical property requirements, in heat bondable acoustical sheets it has generally been found that asphalt based mixtures are particularly suitable for heat bondable sheets. Various mixtures of asphalts and fillers combined with various compositions provide the necessary heat bonding adhesiveness and melt characteristics in the final compositions and are known in the heat bondable art. For example, U.S. Pat. No. 4,287,263 to Woodring discloses a heat bondable sheet material having 30% asphalt, 20% mica, and 50% limestone with a heat deteriorating polyethylene film for stacking capability. U.S. Pat. No. 4,133,932 to Peck discloses a heat bondable material having 45% to 75% asphalt, 5% to 20% of elastomeric modifier and 1.5% to 3.5% of a vegetable oil reaction product.
Due to the belief that the asphaltic type materials were useful in the heat bondable materials for providing selective melt characteristics and inherent adhesive characteristics, and because of the relatively messy and sticky products produced, these materials have generally not been believed to be advantageous in thermoformable type acoustical mat materials due to the flow properties and other undesirable properties which they impart in the compositions. It was believed in the thermoformable art that in order to provide proper thermoformable characteristics which would also result in good physical properties it was generally necessary to provide elastomer based materials having relatively high quantities of elastomeric material with some filler therein.
In recent years the use of ethylene vinyl acetate based elastomer materials has become prevalent in the art of thermoformable acoustical mat compositions. While these materials have been sufficient in physical properties and sound barrier properties, the cost of elastomeric materials, (and particularly the EVA materials), has increased to a dramatic extent in the recent years. Compositions of the past comprised various EVA oil and filler compositions such as shown in U.S. Pat. No. 4,379,190 to Shank; U.S. Pat. No. 4,263,196 to Schumacher; and U.S. Pat. No. 4,508,771 to Peoples. While these compositions are suitable for use as thermoformable acoustical mat compositions, the price of raw material has increased significantly in recent years and costs of producing these compositions has likewise increased.
Acoustical mat products in the market place are usually purchased under long term procurement contracts with automobile companies and the like and as such prices are not readily adjustable to take into consideration cost increases. Thus, in recent years, the profit margins have been reduced dramatically or lost entirely due to the increased cost of these compositions.
Therefore, low cost substitutes for conventional EVA/elastomer based thermoformable mat compositions are in great demand in the industry.
It has therefore been a goal in the art to produce a thermoformable acoustical mat composition which has reduced quantities of EVA and other elastomers used in thermoformable elastomer blends while maintaining or increasing the necessary physical properties of the final thermoformed sheet.
While attempts have been made at reducing EVA contents by increasing filler contents these attempts have generally failed in producing a final product with necessary physical properties for a thermormable sheet or these types of compositions required special machinery or processes for production of such compositions.
In the specification below all percentages are percentages by weight unless otherwise stated.